This invention relates to a method in which a predetermined operation is performed by executing a series of instructions constituting a program and to a microcomputer for implementing this method and, for example, to a technology effectively applicable to a microcomputer including a CPU (Central Processing Unit) and a memory on one chip (hereinafter referred to also as a single-chip microcomputer).
The single-chip microcomputer is arranged with required peripheral circuitry around the CPU on one semiconductor substrate and is incorporated with a ROM (Read-only Memory) for storing a program for operating the computer system. A multi-chip microcomputer does not incorporate such a ROM, instead getting the necessary operating program from an external memory (ROM) arranged outside the computer system.
In the above-mentioned signal-chip microcomputer, an instruction stored in main storage such as the program ROM is adapted to be directly read into the CPU. Hence, as a program size grows, it becomes necessary to increase the capacity of the main storage accordingly. However, the increased capacity necessarily expands an occupational area of the main storage in the semiconductor chip, eventually leading to increased production cost.
To solve such a problem, a method is proposed, as disclosed in Japanese Non-examined Patent Publication No. 55-131848, in which a program is stored in an auxiliary storage device in a compressed form and is expanded before being loaded into a main storage.